This invention relates in general to the field of acquiring data from a well-logging tool in a data acquisition system connected to a well-logging tool by an electrical cable, and in particular, to a method and apparatus for correcting the depth index of such data.
Accurate collection of geophysical property data is a key to successful exploration and production of petroleum resources. Based on data such as electrical and nuclear properties collected in a well-bore, as well as the propagation of sound through a formation, geophysicists make an analysis useful in making many important operational decisions. The analysis includes determination of whether a well is likely to produce hydrocarbons, whether to drill additional wells in the vicinity of an existing well, and whether to abandon a well as being unproductive. Geophysicists may also use well-bore data to select where to set casing in a well and to decide on how to perforate a well to stimulate hydrocarbon flow. One method of collecting well-bore geophysical properties is by way of wireline well-logging. In wireline well-logging, a well-logging tool (also often referred to as a sonde) is lowered into a well-bore on an electrical cable, the wireline. The well-logging tool is an electrically powered measurement device that may, for example, collect electrical data, sonic waveforms that are propagated through the surrounding formation, or radioactivity counts. These measurements are usually converted to a digital form and transmitted on the wireline. Well-logging data is normally indexed by the depth at which the measurement was taken.
The accuracy of the data is a crucial element in the value of the analysis of the well-log data and the correctness of decisions made based on that data. Data accuracy depends both on the accuracy of the measurements made and on the accuracy of the depth index.
It would therefore be desirable to have a system and method for correcting discrepancies in the depth index.